There is known a pressing machine (so-called electric servo press machine (pressing machine); the press machine (pressing machine) may be hereinafter referred to simply as “press”) which converts a rotation of an electric servomotor under electronic control into a vertical reciprocating motion of a slide through an intermediation of a power transmission/conversion mechanism (for example, a crank mechanism), and utilizes the vertical reciprocating motion of the slide to perform press working on a workpiece.
A growing number of electric servo presses have been employed due to their advantages in that an operation status thereof can be controlled by software with a high degree of freedom, and the apparatus can be reduced in cost and size.
By the way, when stopping the slide in the electric servo press, the slide is normally stopped through control of the electric servomotor itself.
However, when stopping the slide due to abnormality in the servo such as a servo error and a positional error, or when stopping the slide by issuing an emergency stop signal from an emergency stop device due to button operation performed by a person or detection of intrusion into a dangerous area, the slide needs to be stopped immediately. Therefore, it is necessary to turn OFF supply of drive power to the servomotor and to stop the slide using a brake that is installed separately.
In this case, in the electric servo press, the electric servomotor and the slide are constantly coupled to each other through an intermediation of drive components such as gears, and hence, when stopping the slide, even the rotation of the electric servomotor needs to be stopped.
At this time, as the inertia of the moving body to be stopped becomes larger, it becomes more difficult to stop the moving body, and hence a certain length of time is required to stop the moving body. Thus, in order to meet the demand that the slide be stopped within a period of time which ensures safety as in the case of the emergency stop, a large-capacity brake is necessary. Therefore, the electric servo press machine is increased in size and cost.
Note that, the immediate stop refers to stop of the slide within a period of time which ensures safety after the reception of the emergency stop signal.
In view of the above, Japanese Patent Application Laid-Open No. 2007-319917 discloses an electric servo press machine including a clutch and a brake device provided in a power transmission path as in a case of a conventional mechanical press, in which an electric motor and a crankshaft can completely be disconnected from each other in a physical (mechanical) manner, and at the time of abnormality, the clutch is released to stop the power transmission, and the brake is actuated to perform emergency stop of the press machine.
The electric servo press machine disclosed in Japanese Patent Application Laid-Open No. 2007-319917 includes the clutch and the brake device provided in the power transmission path, and at the time of emergency stop, the clutch is released to stop the drive transmission of the servomotor, and the brake is actuated. With this configuration, the electric servomotor can be excluded from the components to be stopped, and hence the inertia of the moving body to be stopped can be reduced. As a result, the capacity of the brake can be reduced, thereby contributing to suppression of the capacity increase of the electric servo press machine.
However, when the electric servomotor and the crankshaft (slide) are decoupled from each other by the clutch mechanism as described above, the phases of the electric servomotor and the crankshaft are shifted from each other (synchronization therebetween is not achieved). Therefore, when the clutch mechanism is directly connected for the recovery to the normal operation, troubles may occur in the press working after the recovery and further in cooperative working with other apparatus and facilities in a press working line, which is not a stand-alone system but is a system configured in cooperation with other apparatus and facilities.